diag: Switch to usb mode if md session mode is not peripheral mode

While doing switch logging from memory device mode to usb mode
donot perform the switch to usb mode if md session mode is
peripheral mode and session mask is not NULL.

Change-Id: Ibf11dfe2aa147cd49887e19f541f727fd579634d
Signed-off-by: Sreelakshmi Gownipalli <sgownipa@codeaurora.org>